This invention relates to a hydrometallurgical process for the recovery and separation of valuable elements, in particular gold and silver, from a feed material comprising a refractory, intractable or otherwise poorly responding to conventional treatment routes ores, concentrates and other materials. In particular, the process is a process integrated into one or more existing value element extraction processes.
Polymetallic orebodies containing multiple valuable metals at lower grades are becoming increasingly attractive for resource companies to assess their potential for exploitation, despite the greater metallurgical challenge in the recovery and separation of such elements into saleable concentrates or products. This is generally the case for ores containing precious metals such as gold or silver, platinum group metals (PGMs), and other valuable base and rare metals such as nickel, cobalt, copper, rare earth elements (REE) including yttrium and scandium, as well as uranium, thorium, manganese, zinc, cadmium, molybdenum, vanadium, titanium and other minor elements such as vanadium, germanium and gallium.
Current hydrometallurgical process routes for extraction of valuable metals from polymetallic orebodies are described in International Patent Publication No. WO 99/60178, known as the “Kell Process” (see FIG. 1)1, International Patent Application No. WO2014/009928, and Australian Patent Application No. 2013263848 (the contents of each of which are incorporated herein by reference). All of these processes require as the starting material an ore or a concentrate of the ore and produce one or more leach liquors containing dissolved valuable metals and other elements. The Kell Process is typically specifically applied to PGM and base-metal containing concentrates.
The core of the Kell Process route comprises the steps of:                (i) leaching an ore or concentrate made from an ore in a pressure oxidation sulfate leach to dissolve base metal sulfides contained in the ore or concentrate and forming a sulfate leach filtrate containing base metals and a residue containing platinum group metals (PGMs);        (ii) separating the sulfate leach filtrate from the residue;        (iii) roasting or heat treating the residue to form a calcine; and        (iv) leaching the calcine in a chloride leach to dissolve the PGMs into solution forming a chloride leach filtrate for PGM recovery and a solid waste residue.        
However, a wide range of feed materials, in particular comprising refractory gold or silver-bearing ores or concentrates containing the precious metals gold or silver are problematic in that they return low recoveries of these metals, rendering conventional process routes such as cyanidation uneconomic or otherwise technically unsuitable for treatment of these materials2.
These refractory or intractable ores, concentrates and other materials can be classified to fall into several categories, including:                1. Conventional refractory sulfides (gold or silver particles are smaller than conventional grind sizes and are encapsulated in various sulfide minerals)—typically treated by pressure or bacterial oxidation, roasting and/or ultrafine grinding;        2. Sub-microscopic refractory sulfides (sometimes referred to as “solid solution”)—(gold or silver particles are so much smaller than conventional grind sizes that they cannot be observed using scanning electron microscopy and are encapsulated in various sulfide minerals)—typically treated by pressure or bacterial oxidation or roasting;        3. “Preg-robbing” materials (carbonaceous matter or other sorbent minerals such as clays are present that may lower gold and silver recoveries by adsorbing or “preg-robbing” the leached gold and silver from cyanide leach solutions)—typically treated by roasting or blinding with kerosene along with use of stronger cyanide solution and higher carbon addition;        4. Carbon-locked materials (carbonaceous matter such as kerogen is present that may lower gold and silver recoveries by physical encapsulation)—typically treated by roasting;        5. Double refractory sulfides (gold or silver particles are smaller than conventional grind sizes and are encapsulated in various sulfide minerals; carbonaceous matter or other sorbent minerals are also present that may lower gold and silver recoveries by physical encapsulation or “preg-robbing” from cyanide leach solutions)—typically treated by roasting or alkaline pressure oxidation;        6. Calcine tailings (residue after roasting and subsequent cyanide leaching of concentrates or ores, containing gold or silver physically encapsulated in the remaining matrix)—typically not treatable using conventional methods;        7. Silicate or aluminate-locked materials (alumina/siliceous matter or phases are present that may lower gold and silver recoveries by physical encapsulation, coating or adsorption)—typically not treatable using conventional methods;        8. Refractory material considered to bear microclusters containing gold or PGMs (e.g. “nanogold”, “nanodimensional gold”, “aurides”, etc, that may also involve other elements such as Al, Si, Ti, V, Zr, Nb, Hg, Mo, W, Ag, Cu, Cs, La, etc; at which scale the bonds may be stronger than those between bulk atoms and hence the chemical behaviour of precious metals may be altered by the so-called “glue” effect)—typically not treatable using conventional methods;        9. Slags (residue after smelting of concentrates or ores, containing gold or silver physically encapsulated in the remaining matrix)—typically not treatable using conventional methods;        10. Amalgamation tailings (residue after mercury amalgamation of concentrates or ores, containing gold or silver physically encapsulated in the remaining matrix)—typically treated using roasting, along with stronger cyanide addition; and        11. Refractory mineral phases in ores containing gold or silver (examples include various slow or poorly cyanide-leaching minerals such as electrum Au—Ag, acanthite Ag2S, aurostibite AuSb2, calaverite AuTe2, sylvanite (Ag,Au)Te2, amongst others—typically treated using roasting or lime boil, along with stronger cyanide addition;        12. “e-Waste”, spent catalysts and other precious-metals bearing wastes (a variety of such material with a range of metallurgical response characteristics is becoming increasingly available)—typically treated by a wide range of mechanical separation, pyro-metallurgical, hydrometallurgical, and bio-hydrometallurgical technologies;        13. Specific non-refractory concentrates (in particular, instances where the concentrates are low-grade, contain elements deleterious to conventional processing or the resource is too small to warrant a stand-alone treatment facility)—typically not treatable using conventional methods unless a toll treatment arrangement can be made with a suitable facility.        
Using conventional methods would require a distinct and separate flowsheet to be developed and a stand-alone plant to be built for each material type and in some cases the material is not considered economically treatable using current available technology because ores contain a combination of categories of the above types of refractoriness.
An integrated process for treatment and recovery of value elements including precious, base and rare metals, and particularly gold or silver from any or a combination of these materials is therefore needed, rather than requiring a stand-alone plant to be built for each material type. It would further be useful if such a process was able to be integrated into the existing processes at plants, such as into the core Kell Process (as claimed in International Patent Publication No. WO 99/60178), or a modified Kell process (as claimed in either International Patent Application No. WO2014/009928, or Australian Patent Application No. 2013263848), or into other base and precious metals extraction processes, such as Heap Leaching, thereby benefiting from savings in capital, operating and infrastructure costs. A process whereby high-grade value metal concentrates or individual value metal products are produced onsite offers considerable financial benefit by eliminating refining charges.
Furthermore, the use of cyanide, a toxic chemical that is conventionally used in gold and silver processing and requires increasingly stringent control measures to satisfy tightening safety and environmental concerns from stakeholders and the community is problematic. An alternative process that does not require its use would be useful. Moreover, conventional processes generate SO2 and other pollutants which are detrimental to the environment and an alternative, environmentally responsible method is needed3.